This invention pertains to a green ceramic precursor powder which is useful in the preparation of preceramic greenware.
It is known to prepare ceramic greenware by extruding a solution or paste containing a metal oxide. U.S. Pat. No. 2,776,898, for example, discloses an extrudable paste comprising barium titanate, an organic binder such as polystyrene, and optionally a solvent for use in fabricating ceramic dielectrics. U.S. Pat. No. 2,952,877 discloses an extrudable formulation comprising powdered metal oxide particulates, a water-soluble polymeric organic binder, and a water-soluble plasticizer for use in making ceramic insulators. U.S. Pat. No. 3,885,977 teaches a composition comprising a mixture of blended oxides, water, binders, and plasticizers. The composition can be extruded into monolithic honeycombs and fired.
It is also known to prepare ceramic greenware by injection molding a solution or paste containing a metal oxide. U.S. Pat. No. 4,624,812 discloses a composition comprising a ceramic powder such as calcium oxide-stabilized zirconium oxide, and a binding agent such as polyacetal. The composition can be injection molded and then sintered to form a dense ceramic. U.S. Pat. No. 4,345,955 discloses an injection moldable mixture comprising barium titanate and a binder, such as polyethylene, for use in manufacturing multilayer capacitors.
Extruding or injection molding a nonmalleable solid, such as an inorganic oxide, into a green ceramic body is difficult. A variety of green-body defects can arise during the process, such as surface and edge tears, core cracks, and lamination. Prior to extrusion, it is necessary to mill the solid extensively to a finely divided powder in order to maximize uniformity of composition and minimize extrusion defects. However, if the solid is a multi-metal mixture, for example of two or more metal oxides, the composition of the extruded green body may vary even after extensive prior milling.
It would be advantageous to have a green ceramic powder which is capable of being melt processed, as in extrusion, compression molding, or injection molding, into ceramic greenware of uniform composition. It would be more advantageous if the melt processed greenware could be prepared without extensive prior milling.